According to Penrose, the basic premise in twistor theory is that light rays are to be
regarded as more basic entities than spacetime events (see e.g. [1]}).
Consider real, 4-dimensional Minkowski spacetime \(\mathbb {M}\) , and a point with coordinates \(x^{AA^{\prime }}_{o}\) 
(with respect to an arbitrary origin).
A light ray \(\gamma \)  through this point is described by the null geodesic
\(x^{AA^{\prime }}(\tau )=\tau \lambda ^{A}\bar{\lambda }^{A^{\prime }}+x^{AA^{\prime }}_{o},\) 
